Multiplex receiving apparatus



Patented Mar. 19, 1935 MULTIPLEX RECEIVING APPARATUS Alfred Kahn, OzonePark, N. Y.,'assignor to Radio Corporation of America, a corporation ofDelaware This invention relates to multiplex telegraph receivingsystems, and has for its principal object to provide, in such a system,a method of and apparatus for easily and eiiiciently assigning thereceived signals to the diierent channels. More specically, an object isto provide a receiving system which is simple in construction, easy tomaintain and which requires a mininum number of parts. y

The present invention, although 'not limited thereto, finds particularapplication to multiplex systems of the time division type, and for thisreason the invention will be described with special regard thereto. Inmultiplex systems of the time division type the successive-basic unitsof each channel are divided into equal portions of like number as theseveral channels, and the transmittingI circuit is assignedlconsecutively to successive channels for a time interval Aequal at mostto one of these portions, the remaining portion of each basic unit ofeach channel being discarded and subsequently restored at thereceivingend of the circuit. Such a multiplex arrangement is described in UnitedStates Patent No. 1,979,484, granted November 6, 1934, to R. E. Mathes.

In brief, the present invention comprises a coupling system forassigning the received incoming signals to their respective channels,and for enabling the received signals to be rebuilt to their originalform as at the transmitting station', whereby the suppressed portions ofthe transmitted signals are restored. For eecting this purpose, use ismade of a coupling electron discharge device whose normal condition ofelectrical stability is changed upon the iiow of signal currents -in theinput circuit of the receiving arrangement.

Referring to the single drawing accompanying this specification, thereis shown a receiving circuit arrangement for a multiplex system inaccordance with the present invention. This 4arrangement comprises,essentially, an energy collector or antenna 1, an ,amplifier anddetector circuit 2 adapted to receive radio frequency energy from theantenna and to "'detect same in a manner Well known in the art, a tonekeyer 3 under control Q f apparatus 2 for transmitting over a land line4 to the -receiving station A audible frequency tone which isinterrupted in accordance with received signal energy, an amplier andrectier circuit 5 for producing the envelope of the keyed tone, couplingtube 6 and a so-called kicker arrangement 7 with associated apparatusvfor assigning the incoming signals to their re- Appliation `February z5,1933, serial No. 658,620

c claims. 101. 17a-50) spective channels, each of the channels having -alocking circuit 8 for rebuilding the received ent No. 1,874,866, grantedto I-I. H. Beverage, et v al., particularly jthat portion which relatesto Figure 2 thereof.

Similarly, ampliner-detector apparatus 5, which also is of a well knowntype, has been indicated in box form, the output or full wave rectifierpart only being shown in order to' illustrate its manner of connectionto the coupling tube 6. Only the negative pulses of the rectified signalare applied to the grid of tube 6 since the positive end of therectifier is tied down to. the filament which is at ground or zeropotential. A low pass filter 9 consisting of series inductance and shuntcapacitance is utilized for smoothing out whatever tone componentsremain in the rectified signal.

In the circuit diagram shown, coupling tube 6 is biased bymeans of agrid battery 10 to pass current normally, in which cndition there existsa positive potential on its anode which is lower in v'alue than thepotential of the anode supply -l-Eb, due to the IR drop in resistance11. The receipt of a signal pulse on the grid of tube 6, however, isarranged to bias the grid so negatively as to make the tube block, thatis, cease passing current, at which time the voltage on the anode oftube 6 will rise to the maximum value of +En, since at this time nocurrent ilowsv in the resistance 11.

Although this particular manner of operating tube 6 has beendescribed,it will readily be understood that the invention is not limited thereto,since the desired coupling effect canbe obtained in other Ways, forexample, by biasing tube 6 to cut-off at all times except when a signalis impressed on its grid, merely by the use of a reversing tube, or elseby permitting tube 6 to draw current at all times'and changing themagnitude thereof in accerdancewith the incoming signals.

For assigning the incoming signals to their respective channels, thereis provided a rotating kicker disc 7 which may consist of any suitabledistributor arrangement for conductively closing an electrical circuitbetween the output of coupling tube 6 and the different channels insuccession. It is preferred, however, to use a commutator of the typedescribed in United States Patent 1,963,587, granted June 19, 1934, toR. E. Mathes. In the particular arrangement shown,

\disc 7,. comprises an insulating drum having attached to its peripherymetallic wipers or brushes 12 which are arranged, as they revolve, tomomentarily bridge, in succession, a plurality of pairs of contacts 13,14, and thus close a circuit from tube 6, which is associated with allof the contacts 13, to the respective channels which are individuallyconnected through condensers 15 to the diierent contacts 14. Only twochannels have been shown, but it will be understood that any desirednumber may be used. Kicker disc 7 is driven by a motor, not shown, whichis maintained in synchronism by the incoming signals. Although any wellknown method of synchronism may be utilized it is preferred to employthe system described in a'copending application of R. E..

Mathes, Serial No.' 645,171, filed December 1, 1932.

In each receiving channel and in circuit with its respective condenser15 is a locking circuit 8 for restoring the receiving signalsto theiroriginal form as they appeared before transmission. Since the lockingcircuit apparatus in each channel is the same, for the sake ofsimplicity, only a single channel circuit has been shown and will bedescribed herein. The locking lcircuit comprises ltwo electron dischargedevices 16, 17 which are arranged to, have two degrees of electricalstability. These tubes are unstable when both are drawing current, butstable when one ltube is passing current and the other blocking. Thechanging from one condition of stable equilibrium, such as when tube 16is blocking and tube 17 is passing, to the other condition, when tube 16is passing and tube 17 blocking, or the reverse, is caused by thepresence of a suitable potential on the grid of tube 16 which is, due,in this case, to `a. charge on condenser 15, the latter, in turn, beingin circuit with a resistance 1,1 connected to the anode of tube 6, Vanda resistance.19 in the grid circuit of tube 16 of the locking circuit.This locking circuit is more adequately described in UnitedStates Patent1,844,950 granted February 16, 1932 to J. L. Finch to which reference ismade for a more detailed explanation of the operation thereof.

Coupled to the output terminals of the locking I circuit 8 may be anytype of utilization circuit key an audible tone for transmission overland line 4 to the receiving station A at which the interrupted tonesignals, corresponding to the incoming messages, are rectified and theenvelope of the signals applied to the grid of tube 6. Filter 9 is usedto smooth out any of the tone components remaining in therectiiiedsignal. The application of the rectified signals on the grid of tube 6drives the grid negative and causes the current will flow throughresistance` 11, and the plate will be at its maximum positive potential.The kicker 7, which is driven in synchronism with the incoming signal,will now'close the circuit from the anode of tube 6 through contacts 13and 14, over brush or pin 12, to the condenser 15, thus charging thecondenser. The application of this charge to condenser 15 causes amornentary :dow of charging current4 into the condenser through acircuit including anode resistance 11 and grid resistor 19 of thelocking circuit, thus enabling the application of a pulse of suchpolarity to the grid end of resistance 19 which will drive the grid oftube 16 positive. Tube 16 will now draw current, and due to -thecharacteristics of the locking circuit 8, tube 17 will be blocked. Anelectrical pulse of a predetermined polarity will thus be transmitted toutilization'means 18 over lead 20. This pulse will continue untiLtheconditions of tubes 16 and 17 of the locking circuit reverse, at whichtime tube 16 will block and tub e 17 pass current over lead 21 vto theutilization circuit.

Now, if at the next time the channel under consideration is assigned tothe coupling circuit a signal is again being impressed on the gridof thecoupling tube 6, condenser 15 will remain charged and tube 16 of thelocking circuit will continue' to pass current. However, if at the timethe channel is assigned to the circuit no signal is impressed on thegrid of coupling tube 6, then anode current will iiow again throughresistance 11 and will cause a drop of potential thereacross at theinstant the contacts 13 and 14 are bridged by brush 12 of the kicker 7.Condenser 15 will now discharge over a path traced from Ea grid resistor19, through contacts 13, 14 and wiper pin 12, and into tube 6, thuscausing the grid end of resistance 19 to become negative and allowingtube 17 to pass current while tube 16 blocks. In this manner, there isobtained a push-pull output eiect which operates the utilization means,and reproduces the original signal characters transmitted, which may beof the Morse code or any other suitable type.

It will be understood, of course, from a mere inspection of the drawingvthat the invention is not limited to radio systems or to the precisearrangement of parts shown since land line systems may well be used andvarious modifications made in thecircuitsillustrated and describedherein without departing from the spirit and scope of the appendedclaims.

1. A receiving circuit for a multiplex telegraph system comprising arectifying system for rectifying the received signals and having anoutput circuit, an electron discharge coupling device associated withsaid outp'ut circuit, circuit closing means for connecting atpredetermined intervals the output of said coupling device to thevarious channels, said device being arranged to change its normalcondition of electrical stability upon the iiow of signal current insaid rectifying system,` storage means in eachof said channels, thestate of which is dependent upon the condition of said electrondischarge device at the instant said device is connected through saidcircuit closing means to its associated channel, and utilization meansindividual to each channel under vthe control of said storage means.

2.. A receiving circuit for a multiplex telegraph system comprising arectifying system for rectifying the received signals and having anoutput circuit, an electron discharge coupling device normally biasedabove cut-off to pass current associated with said output circuit, saiddevice being arranged to become temporarily biased below cut-off uponthe ow of signal current in said rectifying system, storage means,circuit closing means for connecting the output of said electrondischarge device at predetermined intervals to said storage means, andutilization means in circuit with said storage means.

3. A receiving circuit for a multiplex telegraph system comprising arectifying system for rectiying the received signals and having anoutput circuit, an electron discharge coupling device normally biasedabove cut-oi to pass current associated with said output circuit, saiddevice being arranged to become temporarily biased below cutoff upon theflow of signal current in said rectifying system, a condenser, means forconnecting the output circuit of said electron discharge device atpredetermined intervals to said condenser, and utilization means incircuit with said condenser.

4. A receiving system for a multiplex telegraph system comprising arectifying system for rectifying the received signals and having anoutput circuit, an electron discharge coupling device normally biasedabove cut-off to pass current associated with said output circuit, saiddevice being varranged to become temporarily biased below cut-off uponthe flow of signal current in said rectifying system, storage means,circuit closing means for connecting the output circuit of said electrondischarge device at predetermined intervals to said storage means, asignal rebuilding system under control of said storage means comprisinga plurality of electron discharge devices whose anodes and controlelectrodes are respectively interconnected, and a utilization circuitconnected to said signal rebuilding system.

5. A receiving circuit for a multiplex telegraph system comprising arectifying system for rectifying the received signals and having anoutput circuit, an electron discharge coupling device normally biasedabove cut-off to pass current associated with said output circuit, saiddevice being arranged to become temporarily biased below cut-oi-upon theflow of signal current in said rectifying system, a condenser individualto each channel of the telegraph system, circuit closing means forconnecting the output 'circuit of said electron discharge device atpredetermined intervals to each of said condensers, signal rebuildingsystems under control of said condensers comprising a plurality ofelectron discharge devices whose anodes and control electrodes arerespectively inter-connected, and a utilization circuit coupled to eachof said signal rebuilding systems.

6. A receiving system for a multiplex telegraph system comprising arectifying system for rectifying the received signals and having anoutput circuit, an electron discharge coupling device normally biasedabove cut-off to pass current connected to said output circuit, aconnection from the anode of said electron discharge device to a sourceof positive potential, a resistance in said connection, a pair ofcontacts one of which is directly connected to said anode and the otherof which is connected to a terminal of a condenser, circuit closingmeans for conductively connecting at predetermined intervals said pairof contacts, a signal rebuilding system connected to the other terminalof said condenser comprising a plurality of electron discharge deviceswhose anodes and control electrodes are respectively inter-con-- nected,and a utilization circuit coupled to said signal rebuilding system.

ALFRED KAI-IN.

